Under a microscope, human sperm seem to swim like buzzing eels, tails swirling back and forth as they search for an egg to fertilize.
But now, new 3D microscopy and high-speed video reveal that sperm don’t swim at all in this simple, symmetrical motion. Instead, they move with a rotating rotation, which compensates for the fact that their tails actually beat on one side only.
“It’s almost like being a swimmer, but you could only swing your leg to one side,” said study author Hermes Gadêlha, a mathematician at the University of Bristol in the UK. “If you did this in a pool and you only did it on one side, you will always swim in circles … Nature in its wisdom came [up] with a very complex, ingenious way to move forward. ”
Connected: Sexy swimmers: 7 facts about sperm
The first person to observe human semen closely was Anthony van Leeuwenhoek, a Dutch scientist known as the father of microbiology. In 1677, van Leeuwenhoek converted his newly developed microscope to his own semen, seeing for the first time that the fluid was filled with tiny, fluttering cells.
Under a 2D microscope, it was clear that the semen was driven by tails that seemed to sway toward each other as the sperm’s head rotated. For the next 343 years, this was the understanding of how human sperm move.
“[M]every scientist has postulated that there is likely to be a very important 3D element in how the sperm tail moves, but to date we have not had the technology to reliably perform such measurements, “said Alan Pacey, a professor of andrology at the University of Sheffield. in England, who did not participate in the research.
Thus, the new study is a “significant step forward,” Paisi wrote in an email to Live Science.
Gadêlha and his colleagues at the Universidad Nacional Autónoma de México have begun research into a “blue sky study”, Gadêlha said. Using microscopic techniques that allow three-dimensional imaging and a high-speed camera that can capture 55,000 frames per second, they recorded human sperm floating on a microscope slide.
“What we found was extremely surprising because it completely broke with our belief system,” Gadelha told Live Science.
Connected: The 7 greatest mysteries of the human body
The tails of the sperm did not shake, they looked like a whip on the side. Instead, they could only win in one direction. To push forward from this asymmetrical movement of the tail, the head of the sperm rotates in an oscillating motion at the same time as the rotation of the tail. The rotation of the head and tail are actually two separate movements controlled by two different cellular mechanisms, Gadêlha said, but when combined, the result is something like a rotating otter or a rotating drill. In the course of 360-degree rotation, the movement on one side of the tail is equalized, adding to the forward drive.
“The semen doesn’t even swim, the semen breaks into the liquid,” Gadelka said.
The researchers published their findings today (July 31st) in the journal Scientific progress,,
Asymmetry and fertility
Technically, how sperm moves is called precession, which means that it rotates around an axis, but this axis of rotation changes. The planets do this on their rotational orbits around the sun, but a more familiar example is a rotating countertop that swings and dances on the floor as it spins on top.
“It’s important to note that during the journey to the egg, the sperm will swim through a much more complex environment than the drop of fluid in which they were observed for this study,” Paisi said. “In a woman’s body, they will have to swim in narrow canals with very sticky fluid in the cervix, walls of wavy cells in the fallopian tubes, as well as deal with muscle contractions and fluid being pushed along the length (from the swinging tips of cells called cilia) in the opposite direction to where they want to go.However, if they are really able to make their way forward, I can now see with much greater clarity how sperm can cope with this attack attempt to get to the egg and be able to get inside it, “Pacey said
Sperm motility or the ability to move is one of the main indicators of fertility that doctors consider when assessing male fertility, Gadêlha said. The rotation of the sperm head is not currently considered in any of these indicators, but it is possible that further research will reveal certain defects that disrupt this rotation and thus stimulate the movement of sperm.
Clinical fertility uses 2D microscopy and more work is needed to see if 3D microscopy can benefit from their analysis, Paisi said.
“Certainly any 3D approach needs to be fast, inexpensive and automated to have any clinical value,” he said. “Nevertheless, this document is certainly a step in the right direction.”
Originally published in Live Science.